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Guide · 25 lessons

Learn: short guides to image formats, file sizes and private files

Short guides, about five minutes each. Every one explains a question that comes up when you work with photos and PDFs, such as why a HEIC file won't open or how many pixels a print needs, says where the facts come from, and ends with a quick check and a link to the tool that does the job in your browser. Each guide shows the date it was last checked. Your reading progress stays in this browser only.

Understand your image and PDF files well enough to make them fit, print well and stay private.

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Module 1 Image formats and compression

HEIC, JPG, PNG, WebP, AVIF and SVG, transparency, colour profiles, screenshots and sideways photos.

  1. HEIC vs JPG: why your iPhone photos won't open everywhereHEIC saves space on the iPhone; JPG opens everywhere. Keep the originals, convert copies when a site or person needs JPG.5 min read✓ Read
  2. JPG, PNG, WebP or AVIF: which image format to usePhotos: JPG for safety, WebP or AVIF for smaller files. Screenshots and text: PNG. Logos: SVG if you have it, otherwise PNG.5 min read✓ Read
  3. Image quality settings explained: what the number really doesThe quality number is a dial for how much detail the encoder may throw away, not a percentage. Compress once, from the best original you have.5 min read✓ Read
  4. The best format for screenshots: PNG, WebP or JPG?PNG keeps text and sharp edges perfectly but makes large files. Keep it for screens full of text, try lossless WebP for a smaller exact copy, and use JPG only for screenshots that are mostly photo.5 min read✓ Read
  5. Image transparency and the alpha channel, explainedTransparency is stored as a fourth channel, alpha, next to red, green and blue. PNG, WebP and AVIF keep it with smooth edges, GIF only on or off, and JPG not at all.5 min read✓ Read
  6. SVG vs PNG: vector and raster images explainedA raster image is a fixed grid of pixels; a vector image is a set of drawing instructions that can be redrawn at any size. Use SVG for logos, icons and diagrams, and raster formats for photos.5 min read✓ Read
  7. sRGB, Display P3 and colour profiles, explainedThe numbers in an image only become exact colours once you know their colour space. A colour profile says which one; when it is dropped, software assumes sRGB, which changes wide-gamut photos.5 min read✓ Read
  8. Why photos appear sideways or upside down, and how to fix them for goodCameras often store the picture as the sensor saw it and add a tag saying how to turn it. Apps that ignore the tag show it sideways. Saving the photo upright fixes it everywhere.5 min read✓ Read

Module 2 Sizes for print, web and social

The pixels a print needs, images that keep websites fast, and aspect ratios for cropping.

  1. DPI and print size: how many pixels you needPixels = inches × DPI. 300 DPI is the common print standard, lower is acceptable for things seen from further away, and the DPI tag alone changes nothing.5 min read✓ Read
  2. Resizing images for a faster website: widths, formats and layoutUpload images about twice as wide as they appear on the page, in a modern format, and give every image a width and height. Lazy-load the ones further down, never the main one.5 min read✓ Read
  3. Aspect ratios explained: 1:1, 4:3, 3:2, 16:9 and when to use themAn aspect ratio is the shape of a picture, width to height. When a photo has to fit a different shape you can crop it, pad it or stretch it, and only stretching distorts it.5 min read✓ Read

Module 3 Photo details and privacy

What photos reveal (location, Live Photos, motion photos) and how in-browser tools keep files on your device.

  1. What EXIF data reveals about your photos, and how to remove itPhotos can carry the date, the camera and, if location is on, the exact place. Switch off location in the camera if you don't want it, and clean files before you share originals.5 min read✓ Read
  2. Live Photos and motion photos: the video hidden in your pictureLive Photos and motion photos record moments before and after the shot, often with sound. Share a still when you only mean to send a picture, and check what a file carries before posting it.5 min read✓ Read
  3. How in-browser file tools keep your files privateThe browser reads the file, WebAssembly code does the work on your device and the result is saved from memory. Test it with airplane mode or the Network panel, and remember the page itself still loads from the web.5 min read✓ Read

Module 4 PDFs: size, scans, passwords and signatures

Why PDFs get big, phone scans, PDF passwords and restrictions, digital signatures and PDF/A.

  1. Why is my PDF so big? What fills it and what compression can doImages are usually what makes a PDF heavy. Re-saving the photos keeps text and links; turning pages into images shrinks scans further but loses text. Text-only PDFs barely shrink.5 min read✓ Read
  2. Scan documents to PDF with your phone: photos, page size and privacyShoot flat pages in even light, fill the frame, choose A4 or US Letter to match where the document goes, keep the file small, and don't upload copies of IDs to sites you don't know.5 min read✓ Read
  3. PDF passwords: open passwords versus permission restrictionsAn open password encrypts a PDF so it can't be read without it. Permission restrictions only ask the reader software to block printing, copying or editing.5 min read✓ Read
  4. PDF digital signatures explained: why any change breaks themA digital signature fingerprints the exact bytes of a PDF. Any tool that rewrites the file changes those bytes, so do all edits before signing and keep the signed original.5 min read✓ Read
  5. PDF/A and PDF versions explained: what an archive-ready PDF needsThe version number tells you which edition of the PDF rules a file follows. PDF/A is a stricter form of PDF made so a document still looks the same decades from now.5 min read✓ Read

Module 5 Forms, uploads and file-size limits

Getting photos, signatures and documents accepted: KB limits, exam and passport photos, email attachments.

  1. Getting a photo under an upload form's size limitLower the quality first, then the pixel size. Treat 1 KB as 1000 bytes to be safe, and never enlarge a photo to reach a minimum.5 min read✓ Read
  2. KB or KiB? Why file size limits are ambiguous and how to stay safeA kilobyte is 1000 bytes by the standard, but some software uses 1024. To pass a form's KB range either way, stay under the maximum × 1000 bytes and above the minimum × 1024 bytes.5 min read✓ Read
  3. Passport photo rules: digital uploads versus printed photosEach authority sets its own sizes and its own editing rules. Check its current page, keep the original file, and remember that no resizer can fix light, shadows or expression.5 min read✓ Read
  4. Photo and signature uploads for IBPS, UPSC, NTA and SSC: sizes and rulesEach exam body sets its own pixel and KB limits, and all four take a live photo during the application. Check the current notice, then make each file to its numbers.6 min read✓ Read
  5. Photographing a signature or document so upload forms accept itSign in dark ink on plain white paper, shoot straight on in even light without zoom, crop tightly, save as JPG, and check the result at full size before you upload.5 min read✓ Read
  6. Email attachment size limits: Gmail, Outlook, iCloud and YahooThe big email services stop at about 25 MB per message, and attachments grow by about a third when sent. Shrink photos and PDFs, combine pages, or share a link for anything bigger.5 min read✓ Read

File formats and official photo rules change. Each guide shows the date it was last checked; for forms and official photos, the authority's own page has the final word.

Free tools for files you have the right to use. Everything runs on your device; check important results (forms, prints, official photos) before you send them. Terms of use.